NAME

       XtAppNextEvent,  XtAppPending,  XtAppPeekEvent, XtAppProcessEvent, XtDispatchEvent, XtAppMainLoop - query
       and process events and input

SYNTAX

       #include <X11/Intrinsic.h>

       void XtAppNextEvent(XtAppContext app_context, XEvent *event_return);

       Boolean XtAppPeekEvent(XtAppContext app_context, XEvent *event_return);

       XtInputMask XtAppPending(XtAppContext app_context);

       void XtAppProcessEvent(XtAppContext app_context, XtInputMask mask);

       Boolean XtDispatchEvent(XEvent *event);

       void XtAppMainLoop(XtAppContext app_context);

ARGUMENTS

       app_context
                 Specifies the application context that identifies the application.

       event     Specifies a pointer to the event structure that is to be dispatched to  the  appropriate  event
                 handler.

       event_return
                 Returns the event information to the specified event structure.

       mask      Specifies  what  types  of  events  to  process.   The  mask is the bitwise inclusive OR of any
                 combination of XtIMXEvent, XtIMTimer, XtIMAlternateInput, and XtIMSignal.   As  a  convenience,
                 the  X  Toolkit  defines  the symbolic name XtIMAll to be the bitwise inclusive OR of all event
                 types.

DESCRIPTION

       If the X event queue is empty, XtAppNextEvent flushes the  X  output  buffers  of  each  Display  in  the
       application  context  and  waits  for  an event while looking at the other input sources, timeout timeout
       values, and signal handlers and calling any callback procedures triggered by them.  This wait time can be
       used for background processing (see Section 7.8).

       If there is an event in the queue, XtAppPeekEvent fills in the event and returns a nonzero value.  If  no
       X  input  is  on  the queue, XtAppPeekEvent flushes the output buffer and blocks until input is available
       (possibly calling some timeout callbacks in the process).  If the input is an event, XtAppPeekEvent fills
       in the event and returns a nonzero value.  Otherwise, the input is for an  alternate  input  source,  and
       XtAppPeekEvent returns zero.

       The  XtAppPending  function  returns a nonzero value if there are events pending from the X server, timer
       pending, or other input sources pending.  The value returned is a bit mask that is the OR of  XtIMXEvent,
       XtIMTimer,  XtIMAlternateInput,  and XtIMSignal (see XtAppProcessEvent).  If there are no events pending,
       XtAppPending flushes the output buffer and returns zero.

       The XtAppProcessEvent function processes one timer, alternate input, signal source, or X event.  If there
       is nothing of the appropriate type to process, XtAppProcessEvent blocks until there is.  If there is more
       than one type of thing available to process, it is undefined which will  get  processed.   Usually,  this
       procedure  is  not  called by client applications (see XtAppMainLoop).  XtAppProcessEvent processes timer
       events by calling any appropriate timer callbacks, alternate input by calling any  appropriate  alternate
       input  callbacks,  signal  source  by  calling  any appropriate signal callbacks, and X events by calling
       XtDispatchEvent.

       When an X event is received, it is passed to XtDispatchEvent, which calls the appropriate event  handlers
       and passes them the widget, the event, and client-specific data registered with each procedure.  If there
       are  no  handlers for that event registered, the event is ignored and the dispatcher simply returns.  The
       order in which the handlers are called is undefined.

       The XtDispatchEvent function sends those events to the event handler functions that have been  previously
       registered  with  the  dispatch routine.  XtDispatchEvent returns True if it dispatched the event to some
       handler and False  if  it  found  no  handler  to  dispatch  the  event  to.   The  most  common  use  of
       XtDispatchEvent  is  to dispatch events acquired with the XtAppNextEvent procedure.  However, it also can
       be used to dispatch user-constructed events.  XtDispatchEvent also is responsible  for  implementing  the
       grab semantics for XtAddGrab.

       The XtAppMainLoop function processes events using XtAppProcessEvent, varying the mask parameter and using
       XtAppPending  to ensure that it has a chance to handle events of all types, i.e., X events, timer events,
       input events and signal sources.  This constitutes the main loop of X Toolkit applications, and, as such,
       it does not return unless XtAppSetExitFlag is called.  Applications are expected to exit in  response  to
       some  user  action.   There  is  nothing special about XtAppMainLoop; it is simply an loop that processes
       events until XtAppGetExitFlag() returns true.

       Applications can provide their own version of this loop, which tests  some  global  termination  flag  or
       tests that the number of top-level widgets is larger than zero before circling back for the next event.

SEE ALSO

       X Toolkit Intrinsics - C Language Interface
       Xlib - C Language X Interface

X Version 11                                       libXt 1.2.1                                 XtAppNextEvent(3)